The present invention relates to polypeptides of a novel CD44 variant and to polynucleotides encoding same. Specifically the present invention relates to oligonucleotides specific for the novel CD44 polynucleotide variant, antibodies specific for the novel CD44 polypeptide variant, a cell hybridoma expressing monoclonal antibodies (mAbs) specific for said RA specific CD44 variant and mAb expressed thereby, and the use of these antibodies and oligonucleotides in the diagnosis and treatment of inflammatory diseases such as rheumatoid arthritis.
The following is a list of references which are intended for better understanding of the background of the present invention:    Aune, T. M., et al., Published EP Application No. 501233 (1992).    Hale, L. P., et al., WO 9409811 (1994)/    Herrlich et al., European Patent No. 538754, (1991).    Jalkanen, S., et al., WO 9500658, (1993).    Koopman et al., J. Exp. Med. 177:897-904 (1993)    Naor, D., et al., Adv. Cancer Res., 71:241, (1997).    Screaton, G. R., et al., Proc. Natl. Acad. Sci. USA, 89:12160, (1992).    Verdrengh, M., et al., Scand J. Immunol., 42:353, (1995)
The cell surface adhesion molecule, designated CD44, has been shown to be implicated in cell-cell and cell-matrix interactions, as well as in cell traffic and cell transendothelial migration.
CD44 is a single chain molecule comprising a conserved amino terminal extracellular domain, a nonconserved membrane proximal region, a variable region expressing various combinations of variant exons, a conserved transmembrane spanning domain and a conserved cytoplasmic tail. The genomic sequence of mouse and human CD44 includes 5 constant exons at the 5′ terminus, and 5 constant exons at the 3′ end. The mouse CD44 gene includes 10 variant exons in the middle of the molecule, designated V1-V10, resulting in a total of 20 exons. The human CD44 gene comprises only 9 of these 10 variant exons (V2-V10) thus comprising a total of 19 exons (Screaton, G. R., et al., 1992). Differential V2-V10 alternative splicing generates many isoforms of CD44 that express various combinations of variant exons (designated exon Vx, x=1-10), which are inserted in the membrane proximal domain and constitute the variable region of the molecule. These molecules are designated CD44 variants (CD44v). To date, a few dozen isoforms of CD44 are known.
In standard CD44 (CD44s, SEQ ID NO:5), constant exon number 5 is spliced directly to constant exon number 16 and therefore this molecule lacks the entire variable region. The resulting protein product is expressed predominantly on hematopoietic cells and therefore, this product is also known as hematopoietic CD44 (CD44H) or standard CD44 product (CD44s product, SEQ ID NO:6). In keratinocyte CD44, the longest CD44 identified so far, exon V3 to exon V10 are inserted in tandem between the two constant regions of the molecule.
The CD44 N-terminus contains the ligand binding site of the molecule. Hyaluronic acid (HA) is the principal ligand of CD44, but other extracellular matrix (ECM) components (e.g. laminin, collagen, fibronectin and chondroitin sulfate) as well as non-ECM constituents (mucosal vascular addressin, serglycin, osteopontin and class II invariant chain) can also interact with the CD44 receptor. Marked accumulation of CD44, and sometimes hyaluronic acid, is detected in areas of intensive cell migration and cell proliferation, as in wound healing, tissue remodeling, inflammation (including auto inflammation), morphogenesis and carcinogenesis.
The involvement of CD44 protein and variants thereof in autoimmune diseases is known. For example, it has been shown that anti-CD44 monoclonal antibodies (mAbs) can ameliorate the severity of experimentally induced autoimmune arthritis in mice (Verdrengh, M. et al. 1995). However, these mAbs are directed against the constant region of CD44 (and are thus designated anti-pan CD44 mAbs shared by all CD44 isoforms). Therefore, such mAbs may also block CD44 expressed on normal cells, which is required for migratory activity of immune and inflammatory cells engaged in microorganism eradication.
Monoclonal Abs directed against various variant regions of CD44 have also been suggested as potential agents for treatment of autoimmune diseases. Herrlich et al. describe mAbs directed against metastasis-specific variants of CD44v surface protein of a rat pancreatic adenocarcinoma (Herrlich et al., 1991). Anti-CD44-monoclonal antibodies, which inhibit T-cell proliferation, were also provided for treatment of various autoimmune diseases (Aune, T. M. et al., 1992). Monoclonal antibodies specific for forms of CD44 containing exon v6 were also reported as being useful for diagnosing inflammatory diseases (Jalkanen, S. et al., 1994). In addition, it has been reported (Hale, L. P., 1992) that administration of a CD44 protein, peptide or derivative can be used for treating various autoimmune diseases.
In an experimental arthritis mouse model (collagen-induced arthritis), injection of one of three different anti-CD44 mAbs, but not of the isotype-matched control mAbs, at disease onset, prevented an increase in footpad swelling and helped to maintain the clinical score at a very low level (Nedvetzki et al. 1999). Each of the three different types of anti-CD44 mAb recognized a distinct constant epitope of the CD44 receptor. All three antibodies displayed a similar anti-arthritic effect.
The involvement of CD44 in malignant processes has also been described (Naor, D., 1997). Anti-CD44 mAbs which were injected into mice, were shown to inhibit or prevent infiltration of various lymphoma and carcinoma cells into their target organs. In addition, transfection of a variant CD44 isoform into non metastatic rat pancreatic adenocarcinoma cells conferred metastatic potential to these cells.